Re: [APML] NGC 7789 posted

["William R. Mattil" <wrmattil@ix.netcom.com>]

Alan Voetsch wrote:

>Folks, please don't be shy. I do not post pictures to get cheap praise.
>I post them to hear your constructive critisicm so I can figure out how
>to work in PS without driving myself (and you) crazy. Let me have it. 
>
>  
>
Alan,

I won't comment on the color because thats a very subjective issue and 
highly dependant on my monitor and settings. But one thing that I have 
noticed that would absolutely driving me nuts is the fundemental image 
quality. It certainly appears to me that one of the following might be 
happening:

1) Your Refractor isn't up to the task ( doubtful IMHO)

2) Polar Alignment problems

3) Guiding Problems

4) Flexure or other unwanted movement.


My reason for mentioning this is that when I look at your "Raw" image 
and look at the four corners I am not seeing  round stars. In fact if I 
didn't know better I would be thinking that you were using a Newtonian 
and have some coma. Furthermore this aberration is not equal in all four 
corners. This same phenomenon is visible in the center of the image as 
well but to a lesser extent. I am confused by this as Refractors = Round 
stars (or so I always thought) so ....... maybe polar alignment ? Since 
you are guiding off-axis one would think that it's not flexure but it 
could still be differntial flexure between the film plane and the 
guiding head.

Is there a slight shadow in the lower right caused by the pick-off mirror ?

Good processing and I like the framing of the object of interest.

Hope this helps.

Regards

Bill

-- 

William R. Mattil	:	http://www.celestial-images.com


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